Commercial and military transport aircraft are typically designed to carry a given load of passengers, cargo or both, at a given range and/or at a given endurance. Occasionally, the range and/or endurance of the aircraft may need to be increased. Such extended range and/or endurance can be accomplished by installing additional or auxiliary fuel tank systems in the aircraft, typically by positioning fuel tanks physically within the aircraft's fuselage cargo space (i.e., that space within the aircraft's pressurized fuselage which is below the passenger deck). Conventional auxiliary fuel tank systems are typically comprised of additional fuel tanks and their respective equipment, manifolds, and harnesses necessary to manage the additional fuel carried in the tanks.
These additional fuel tanks and systems could come in diverse configurations, for example, with tanks installed under the wings, external to the aircraft or with tanks internal to the fuselage. These additional fuel tanks and systems could be configured to directly supply fuel to the engines or to transfer the fuel to other tanks and from there to feed the aircraft engines or be used to control aircraft center of gravity or even to transfer fuel to other aircraft, in flight or to other vehicles, on ground.
Whatever the reasons to install these additional tanks and systems, they should be at most practical to the aircraft operator. Thus, additional tanks and systems which complement an aircraft's main wing tanks should be relatively simple to install, remove, and integrate into the basic aircraft fuel system. In addition, such additional tanks and systems should be relatively simple to maintain.
Auxiliary fuel tank systems are in and of themselves know. For example, it has recently been proposed in U.S. Pat. Nos. 6,889,940, 7,040,579 and 7,051,979 (the entire content of each being expressly incorporated hereinto by reference) to provide auxiliary fuel tank systems that contemplate providing various separate manifold assemblies (e.g., fuel inlet and outlet manifolds, vent manifolds and the like) internally of each tank. By positioning the tanks assemblies in adjacent side-by-side configuration, their respective internal manifolds may be connected together to provide a tank system that can be operatively interconnected with the aircraft's on-board fuel management systems. However, the proposed auxiliary tank systems of these patents may be somewhat sometimes troublesome. For example, the proposed tank systems may require relatively costly precision machining of the respective manifolds as well as relatively expensive assembly of both the tanks and the aircraft. In addition, these proposed conventional auxiliary fuel tanks systems necessarily demand that a high degree of flexibility in the manifold connections be provided so as to assure that the individual fuel tanks (which themselves are of relatively large dimension and heavy weight) are perfectly aligned in a row within an aircraft fuselage in such a way that the manifolds can be properly connected. Potentially therefore, a series of accesses should be provided in such systems so as to ensure that the tanks, manifolds, and their respective connections may be properly inspected against misconnections, leakage and/or damage.
So-called aircraft turn-around time (i.e., the time needed to return a revenue generating aircraft to the flight line after being withdrawn for maintenance purposes) and maintenance costs are of utmost concern to aircraft operators in the aeronautical industry. Thus, although the conventional auxiliary fuel tanks noted previously may be practical for relatively large auxiliary fuel tanks associated with larger aircraft designs, they may be prove to be quite difficult to be embodied in relatively smaller auxiliary fuel tanks associated with smaller aircraft designs due, for example to inadequate access space to install the necessary fuel management equipment by an assembly worker. In addition, these conventional auxiliary fuel tanks may eventually require disassembly and removal of the tanks so as to allow for equipment inspection, repair or replacement, thereby demanding a relatively stiff penalty in both cost and scheduled maintenance down time.
The installation of electrical equipment near or inside such conventional fuel tanks is another subject of concern, when designing fuel system and equipment. The risk of fire, due to contact between fuel or fuel vapors and equipment that potentially causes sparks must be minimized. Thus, for safety reasons, the adoption of “dry bays” is also recommended in auxiliary fuel tank systems so as to provide an installation space for such equipment that is isolated from the fuel and/or fuel vapors. “Dry bays” which are integral to the fuel tanks also make it easier to detect and drain of any leaked fuel even though they may increase tank design and manufacturing costs, add weight and reduce useable fuel quantity. An alternative concept to such “dry bays” includes providing one or more barriers to prevent occasional fuel leakage or diffusion of fuel vapors into the aircraft interior.
Another difficulty that may be encountered in the conventional auxiliary fuel tank systems noted previously relates to the manifolds that interconnect one tank to another so as to transfer fluids in both directions (i.e., into and out of a respective tank). In case of high accelerations or decelerations in a direction generally parallel to the longitudinal axis of the aircraft (and hence the row of auxiliary fuel tanks positioned within the aircraft's fuselage), if the fuel tanks are fluid-connected to one another through one or more manifolds and fuel is allowed to migrate from one fuel tank to another in a cascade fashion, the pressure that responsively develops in the last one of the fuel tanks in that row may reach values well above the tank's structural limits. As a result, a real risk of potentially damaging or even rupturing the fuel tank exists.
It would therefore be highly desirable if aircraft fuel tanks, systems and methods were provided which address at least some (if not all) of the various design concerns and/or considerations noted above with respect to conventional auxiliary fuel tank systems. It is towards fulfilling such a need that the present invention is directed.